Antimonial alloys used in the manufacture of grids for use in automotive batteries have, in recent years, shown a trend toward the use of lower antimonial contents. Antimony is primarily used to impart strength to the alloys for handling soon after the grid is cast and in the pasting operations. Today, grids only 50 mils thick are being cast and antimony levels have dropped from the historical 11% to as low as 2.5 to 3.0%. A direct consequence of this development has been remarkable improvement in the overall performance of the lead acid battery including significant reduction in the water loss in such batteries. However, it has heretofore been believed that alloys containing less than 2.5% antimony would present several problems, specifically in terms of castability and adequacy of strength for subsequent handling, and offer no reduction in gass casting.
A number of patents, see U.S. Pat. Nos. 3,801,310; 3,912,537; 3,990,893; 3,993,480; etc. have described the use of low antimony levels in alloys designed for battery grid production. These patents recognize the desirability of a low antimony lead alloy; however, the softness and lack of castability due to the low antimony content has heretofore been compensated for by the addition of other elements such as selenium and silver, to improve these properties. U.S. Pat. No. 3,993,480 describes an alloy containing 0.5 to 3.5% antimony with quantities of arsenic, tin, silver, copper, selenium and sulfur. U.S. Pat. No. 3,801,310, for example, describes an alloy containing 1 to 3.5% antimony and additional quantities of arsenic, tin, selenium and silver. The alloys of this patent containing below 2% antimony are described as obtaining adequate hardness only by resorting to water spraying, a procedure that is commercially impractical. Lead alloys containing less than about 2.5% antimony have not been produced commercially, however, because no significant decrease in gassing has heretofore been found with such alloys and such low antimony alloys have still had inadequate hardness. Poor castability, inadequate corrosion resistance, and excessive grid growth have also been problems experienced when using such alloys.
In contrast to the prior art, it has now been found that lead alloys containing low amounts of antimony, e.g. about 1.3 to 2.0% antimony, and specific amounts of arsenic, tin, copper and sulfur have a surprisingly good combination of properties. These properties included good castability, adequate hardness for easy handling and pasting, improved water loss characteristics, good corrosion resistance and good grid growth behavior, high cold crank and reserve capacity, and improved shelf life. Therefore, in accordance with this invention, by producing the alloy with controlled limits of antimony, arsenic and tin concentrations, in addition to the other elements mentioned, a low antimonial lead alloy is produced which has sufficient hardness, good castability and pasteability for use in producing battery grids. Further, the grids in accordance with this invention can be used to produce a maintenance free battery, i.e. one in which water loss or "gassing" is acceptably low. Additional advantages of this new alloy are excellent corrosion resistance, good grid growth characteristics, and low drossing rate.